Lithium manganese rich cathode materials (represented as xLi 2 MnO 3 -(1-x)LiMO 2 , where M = Mn, Ni, Co) for Li-ion batteries have gained considerable research interests as they exhibit higher nominal voltage (∼4.0 V) and specific capacity (>250 mAhg −1 ) as compared to commercially available cathodes. In the present work, we have studied the effect of zirconium ion doping in Li 2 MnO 3 and Li 1.2 Mn 0.55 Ni 0.15 Co 0.1 O 2 (layered notation of 0.5Li 2 MnO 3 -0.5LiMn 0.375 Ni 0.375 Co 0.25 O 2 ) cathode. As compared to its undoped counterpart Li 1.2 Zr 0.008 Mn 0.542 Ni 0.15 Co 0.1 O 2 is found to yield superior cycleability, rate capability and voltage fade characteristics. Thus, capacity retention ∼78% is maintained in Zr doped LMR cathode after 100 charge-discharge cycles whereas for undoped LMR <30% capacity is retained after similar number of charge-discharge cycles. We have performed pre and post cycling X-ray diffraction, Raman spectroscopy, impedance spectroscopy, and dQ/dV analyses to understand the effect of Zr doping on the electrochemical performances of these LMR cathodes. We have demonstrated that the cycling induced layered to spinel phase transformation is substantially suppressed in Zr modified LMR cathodes and leads to their improved electrochemical performances. Also, as analyzed using galvanostatic intermittent titration technique, we have found that Zr doping increases the Li + diffusion coefficient and thereby improves the rate performance of the doped LMR cathode.

Surface coating with electrochemically inert materials are found to be fruitful to improve the cycleability and rate capability characteristics of lithium and manganese rich composite cathode materials. In order to understand the structure-property relation between the nature of coating and the electrochemical performance, surface modification of composite cathodes was carried out either by a thin layer of carbon or zirconia particles. Zirconia coating helps to sustain 86% capacity retention after 50 cycles as compared to bare composite which exhibits 68% capacity retention when cycled at 10 mAg −1 . Among 1 wt%, 2.5 wt% and 5 wt% zirconia coated cathode materials, 2.5 wt% zirconia coating exhibits best rate capability. We have demonstrated that the porous particulate ZrO 2 coating improved the capacity retention of the composite cathodes by suppressing the impedance growth at the electrodes-electrolyte interface.Layered-layered (Li 2 MnO 3 -LiMO 2 (M = Mn, Ni,Co)) nanocomposite cathodes are potentially attractive material candidates for high energy density lithium ion rechargeable batteries. In contrast to traditional layered oxide based cathodes; these composite cathodes are manganese rich and lithium ions are present both in regular lithium as well as in transition metal sites. 1-7 Through some of our recent publications we have established that in xLi 2 MnO 3 -(1-x)Li(Mn 0.375 Ni 0.375 Co 0.25 )O 2 (x < 0.5) composite cathodes Li 2 MnO 3 like nano-domains are structurally integrated in LiMnO 2 layered matrix. 8-10 This lithium and manganese rich compositions form Li 2 MnO 3 domains which are closely interconnected and structurally integrated on the atomic level with layered LiMO 2 (where M = Mn, Co, Ni) and coexist with them. Thus, these lithium and manganese rich compositions can be represented in two component notation as xLi 2 MnO 3 -(1-x)LiMO 2 . In spite of yielding high discharge capacities (>230 mAhg −1 ) these cathodes are plagued with poorer rate capability and fading of capacity with repeated charge-discharge cycling. In one of our earlier publications, we have reported that both the rate capability and the cycleability of these composite cathodes are dependent on the Li 2 MnO 3 content. 8 The rate performance can be improved by reducing the lithium ion diffusion length. Thus, use of nano crystalline electrode materials is suggested to be fruitful. 11 Especially in their charge state, the reactivity of these nano-crystalline composite cathodes with liquid electrolyte is increased substantially. Eventually, the reaction product forms a solid electrolyte interface (SEI) layer on the cathode surface. Due to its poorer electronic conductivity, the SEI layer impedes lithium ion movement during intercalation and de-intercalation. Additionally, the charge transfer resistance during lithium ion intercalation is also increased due to the formation of SEI layer. We had demonstrated that the charge transfer resistance (R CT ) increases with Li 2 MnO 3 content (probably due to its poor electronics conductivity)...

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